Pond construction costs can be highly variable. On a per-acre basis, large ponds are much cheaper to build than small ones. Data at the Alabama Fish Farming Center in Greensboro indicate that watershed ponds larger than 15 acres cost less than $1,000 per acre to build in ideal locations.
This includes clearing, earth fill, excavation, pipe and valve, concrete, seeding and dam gravel. Ponds smaller than 10 acres may cost as much as $1,800 per acre. Ponds on poor sites, i.e., on sites that are steep and require large dams to impound relatively small acreages, may cost $10,000 or more per acre.
The largest cost of building a pond is earthmoving. All other costs are relatively minor. Contractors in commercial catfish areas currently charge $.70 to $1.25 per cubic yard of dirt moved. Costs will no doubt continue to rise as machinery, fuel and labor costs increase.
Pond construction equipment may include the following: large and small bulldozers for clearing and final dressing of levees; self-loading scrapers or tractor-pulled pans; laser leveling and welding equipment; backhoes and hydraulic excavators; farm tractors with soil implements such as cultivators or discs; and a sheepsfoot roller (Fig. 3).
Building a watershed pond:
Following the pond design, begin by flagging the dam, emergency spillway, contours for the top of the riser, top of the dam, and the emergency spillway elevation. (Fig. 4) The contour for the top of the riser will become the actual shoreline. The dam will be built at the same elevation as the top of dam contour around the pond.
The first step in actual earthmoving will be site preparation. This involves clearing trees, removing stumps and roots, and stockpiling the topsoil which can be used to dress the dam later. Trees, stumps and roots should never be buried inside the pond or near the dam.
Some landowners have used portable saw mills to recoup some of the costs of removing valuable timber. Check with a local power saw shop for names. The next step is dam construction. A cutoff trench is excavated along the centerline of the dam; it extends up each abutment as far as there is any pervious material that might allow seepage (Fig. 5).
Any potential seepage must be prevented to avoid water loss and failure of the dam. The bottom of the trench should be at least 8 feet wide with sides no steeper than 1:1. Old stream channels running through the dam should be cleaned out. All stones, gravel, sand, sediment or anything else that would prevent bonding of the earth fill and dam foundation must be removed.
Before filling the cutoff trench with the best available clay soil, the trench may have to be pumped out and lightly scarified. The clay fill should be compacted tightly as each layer is added to the trench. If properly compacted, the clay will strengthen the dam.
Eventually the trench will be filled and then the remaining dam core will be constructed above ground. The core of the dam must be as high as the permanent water elevation. Allow 5 to 10 percent for settlement.
Soil moisture and compaction:
Good compaction requires suitable moisture and compactive effort. The dam must be built gradually in layers of 6 to 8 inches and each layer packed with heavy equipment or sheepsfoot rollers.
The soil used in the dam must be free of all vegetation, roots and large rocks. Soil moisture is critical. Soil too wet or too dry will not adequately compact no matter how many times it’s run over. If the soil is so dry it can’t be hand molded, stop construction or add water with large tank sprayers.
If the soil is so wet that it adheres to construction equipment, stop or, if possible, find drier material. Most dam seepage problems occur because dams were built during drought conditions.
Gregory N. Whitis